Light-emitting diodes based on a carbazole-derivatized dopant: Origin of dopant excitation as a function of the device structure

Efficient green-emitting OLEDs were fabricated by using the carbazole derivative 9-ethyl-N,N'-diphenyl-N,N'-dipyren-1-yl-9H-carbazole-3,6-diamine (C-Et) as a dopant in different layers in a multilayered structure. Depending on the energy levels of the various layers involved, dopant emission can be realized through either energy transfer or the carrier trapping mechanism. By doping into the CBP layer of the device ITO/NPB (40 nm)/CBP:5% C-Et (20 nm)/TPBI (40 nm)/Mg:Ag (50 nm)/Ag(100 nm), a maximum luminance of 48 300 cd/m(2), a maximum quantum efficiency of 3.90%, and a maximum power efficiency of 5.28 lm/W can be achieved.